1. Field of the Invention
The present invention relates to a fluid heating apparatus, more particularly an electromagnetic induction heating type fluid heating apparatus, for heating various types of fluid, such as gas and liquid, to be supplied through piping to a substrate processing section in a substrate processing apparatus which performs required processes upon substrates including semiconductor substrates and substrates for flat panel display.
2. Description of the Background Art
For a substrate processing apparatus, e.g. a reduced-pressure drying apparatus for substrates, it is necessary to heat alcohol vapor, e.g. isopropyl alcohol (IPA) vapor, up to a predetermined temperature to supply the vapor through piping into a chamber in which a substrate is contained under an atmospheric pressure. To heat the IPA vapor, an apparatus has been generally used which comprises a resistance heater on an outer peripheral surface of the piping made of stainless steel or the like and which heats the piping by heat transfer from the resistance heater to indirectly heat the IPA vapor flowing through the piping. Recently, an attempt has been made to heat the fluid flowing through the piping by the use of electromagnetic induction.
FIG. 2 is a schematic vertical sectional view of an apparatus for heating fluid by the use of electromagnetic induction. The fluid heating apparatus of FIG. 2 comprises: a heater case 40 interposed in piping (not shown) through which fluid to be heated is passed; a coil 42 wound about part of an outer peripheral surface of the heater case 40; a power supply unit (not shown) for feeding a high-frequency current through the coil 42; and a heating element 44 disposed inside the heater case 40.
The heater case 40 comprises: a cylindrical part 46 made of a non-magnetic material such as fluororesin; an entrance closing plate 48 having a fluid inlet 50 connected in communication to the piping through which the fluid is passed and a packing 52 for closing a first opening surface of the cylindrical part 46; and an exit closing plate 54 having a fluid outlet 56 connected in communication to the piping through which the heated fluid is fed out and a packing 60 for closing a second opening surface of the cylindrical part 46. Thus, the heater case 40 has an enclosed structure.
The heating element 44, the structure of which is not specifically illustrated, typically comprises a plurality of regularly arranged thin plates, e.g. corrugated plates, made of an electrically conductive material such as ferritic stainless steel so that the fluid flows through the spaces between the thin plates. A temperature sensor 62 includes a temperature sensing element, e.g. a thermocouple 64, inserted in the heater case 40 and disposed downstream from and adjacent to the heating element 44. The temperature sensor 62 measures the temperature of the heating element 44. The heater case 40 is also provided with a temperature sensor 66 for measuring the temperature of the fluid flowing out of the heater case 40. The temperature sensor 66 includes a temperature sensing element, e.g. a thermocouple 68, inserted in the heater case 40 and disposed near the outlet thereof. The temperature sensors 62 and 66 output respective temperature detection signals to a controller not shown. The controller is connected to the power supply unit and an alarm (both not shown).
In the fluid heating apparatus shown in FIG. 2, when the power supply unit feeds the high-frequency current through the coil 42, a magnetic flux is developed to induce eddy currents in the respective thin plates of the heating element 44 in the heater case 40, thereby evolving Joule heat in the thin plates because of the specific resistance of the material of the thin plates, which results in heat generation from the heating element 44. The cylindrical part 46 of the heater case 40, which is made of a non-magnetic material, does not generate heat in itself. The heat generated by the heating element 44 is transferred and applied to the fluid flowed from the piping through the fluid inlet 50 into the heater case 40 during the passage of the fluid through the position of the heating element 44. The fluid heated to a raised temperature flows out of the heater case 40 through the fluid outlet 56 into the piping. In this process, the controller outputs a control signal to the power supply unit, based on the fluid temperature detection signal detected by the temperature sensor 66, to control the temperature of the fluid flowing out of the heater case 40 to reach a target temperature. The controller also compares the temperature near the heating element 44 which is detected by the temperature sensor 62 with a preset warning temperature. When the temperature detected by the temperature sensor 62 exceeds the warning temperature, the controller outputs a signal to the alarm to activate the alarm, and outputs a signal to the power supply unit to control the power supply unit to shut off the supply of electric power from the power supply unit to the coil 42 or weaken the output to the coil 42.
Unfortunately, the conventional fluid heating apparatus as shown in FIG. 2 presents problems to be described below and therefore is not used as a fluid heater for the apparatuses for processing the semiconductor substrates and the flat panel substrates. The conventional fluid heating apparatus comprises the heating element 44 including the plurality of regularly arranged thin plates, e.g. corrugated plates, for the purpose of increasing the heat transfer area of the heating element 44. This results in a complicated structure of the heating element 44 and large amounts of dead space, making it difficult to carry out sufficient initial cleaning of the heating element 44. Further, the thin plates of the heating element 44 are thermally expanded into sliding contact with each other during the heat generation from the heating element 44 or are vibrated under the influence of flow of the fluid, particularly gas, passing through the position of the heating element 44. As a result, a large number of particles are produced by the heating element 44.
Additionally, the heating element 44 must be incorporated into the heater case 40 which is enclosed, with the fluid inlet 50 and the fluid outlet 56 connected in communication to the piping, and which has the coil-wound part made of a non-magnetic material. Thus, the heater case 40 has a complicated structure including flanged parts and the like, which leads to a large number of locations in which contaminants such as particles are deposited. As a result, once the inside of the heater case 40 is contaminated by the particles or the like, it is impossible to easily remove the particles. Therefore, the conventional fluid heating apparatus is disadvantageous in being incapable of suppressing the generation of the particles.
Furthermore, the conventional fluid heating apparatus has a complicated structure such that the heating element 44 including the plurality of thin plates, e.g. corrugated plates, is incorporated in the heater case 40. Such a complicated structure causes the flow of fluid passing through the heater case 40 to stay at some locations to prevent the uniform heat exchange of the entire heating element 44 with the fluid. As a result, the heating element 44 is partly overheated to melt, thereby suffering damages, or is reduced in heat exchange efficiency. Thus, the conventional fluid heating apparatus is not capable of heating the fluid as desired to have the heat transfer area greater than necessary, resulting in increased costs.
Even if an attempt is made to monitor the temperature of the heating element 44 which reaches the highest temperature in order to ensure an explosion-proof property, it is structurally difficult for the conventional fluid heating apparatus to place the thermocouple 64 of the temperature sensor 62 in contact with the heating element 44. Hence, the temperature sensor 62 measures the temperature near the heating element 44. It is therefore difficult to correctly monitor the temperature of the heating element 44. If the thermocouple 64 were placed in contact with the heating element 44 to measure the temperature of the heating element 44, the vibration of the heating element 44 would hinder the thermocouple 64 from making a correct measurement or generate particles to contaminate the fluid. Thus, when heating the flammable fluid such as IPA, the conventional fluid heating apparatus finds difficulties in ensuring the explosion-proof property without contamination of the fluid.
The present invention is intended for a fluid heating apparatus interposed in piping through which fluid to be heated is passed for heating the fluid by using electromagnetic induction.
According to the present invention, the fluid heating apparatus comprises: a heat-generating bent tube formed of an electrically conductive material in a tubular configuration and having opposite ends connected in communication to the piping through which the fluid is passed; a coil provided outside the heat-generating bent tube and wound to surround the heat-generating bent tube; and a power supply unit for feeding a high-frequency current through the coil.
In the fluid heating apparatus according to the present invention, when the power supply unit feeds the high-frequency current through the coil, a magnetic flux is develop to induce an eddy current in the heat-generating bent tube disposed inside the coil and lying within the magnetic flux. Thus, Joule heat is evolved in the heat-generating bent tube because of the specific resistance of the electrically conductive material of the heat-generating bent tube, which results in heat generation from the heat-generating bent tube. When the fluid having flowed through the piping enters the heat-generating bent tube heated to a raised temperature, the fluid is directly heated by the heat-generating bent tube while passing through the inside of the heat-generating bent tube. Then, the fluid heated to a raised temperature flows out of the heat-generating bent tube into the piping.
The heat-generating bent tube which is merely of a tubular configuration allows sufficient initial cleaning of the inner surface of the heat-generating bent tube for contact with the fluid. The heat-generating bent tube is merely a single tube which has no locations which cause particles to be generated in the path of the fluid and has a few locations in which contaminants such as particles are deposited. Therefore, few particles are generated in the path of the fluid in the fluid heating apparatus according to the present invention. Additionally, since the fluid flows merely through the tubular heat-generating bent tube, the heat-generating bent tube exchanges heat throughout its entire area with the fluid uniformly. Thus, the heat-generating bent tube has no overheated portion. Moreover, there is no reduction in efficiency of heat exchange between the heat-generating bent tube and the fluid.
Preferably, in the fluid heating apparatus, the heat-generating bent tube is of a helical configuration; the coil is provided in coaxial relation with the heat-generating bent tube; and the opposite ends of the heat-generating bent tube are electrically connected to each other by an electrically conductive member.
In this fluid heating apparatus, the heat-generating bent tube which is helical (coiled) in coaxial relation with the coil produces an induced electromotive force when the high-frequency current flows through the coil. Then, current flows through a closed circuit formed by the coiled tube and the electrically conductive member since the opposite ends of the coiled tube are connected to each other by the electrically conductive member. Consequently, in the heat-generating bent tube is evolved Joule heat resulting from the current flowing through the tube because of the specific resistance of the electrically conductive material of the tube, in addition to Joule heat resulting from the eddy current. Thus, the efficiency of heat generation from the heat-generating bent tube with respect to the high-frequency current fed through the coil is increased. Therefore, the fluid heating apparatus can heat the fluid more effectively. Moreover, although voltage is developed by the induced electromotive force in the coiled tube, the opposite ends of the coiled tube are short-circuited to each other. Thus, direct contact of a tube temperature sensor with the surface of the heat-generating bent tube for measurement of the temperature of the heat-generating bent tube does not destroy the tube temperature sensor.
Preferably, the fluid heating apparatus further comprises: a tube temperature sensor for detecting the temperature of the heat-generating bent tube; and a controller for effecting predetermined control based on a temperature detection signal from the tube temperature sensor.
In this fluid heating apparatus, the tube temperature sensor detects the temperature of the heat-generating bent tube, and the controller effects required control including, for example, activating an alarm or shutting off the supply of electric power from the power supply unit to the coil, based on the temperature detection signal. Unlike the conventional fluid heating apparatus in which temperature near the heating element is measured, the fluid heating apparatus according to the present invention employs the tube temperature sensor to detect the temperature of the heat-generating bent tube itself, for example, by placing a temperature sensing element, e.g. a thermocouple, in direct contact with the outer peripheral surface of the heat-generating bent tube. The temperature of the fluid flowing through the heat-generating bent tube is always lower than the temperature of the heat-generating bent tube which is detected by the tube temperature sensor. This ensures the temperature control of the fluid, e.g. IPA vapor, below its ignition point.
It is therefore an object of the present invention to provide a fluid heating apparatus for use in heating gas and liquid in an apparatus for processing semiconductor substrates and flat panel substrates, which can suppress the generation of particles in a path of fluid to be heated, which is simple in construction without danger of damages to a heating element in an overheated portion, and which can prevent the reduction in efficiency of heat exchange between the heating element and the fluid to achieve heating of the fluid as desired.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.